Unconventional resources are resources whose exploitation requires a higher-than-average level of technology or investment.
The three largest types of unconventional gas resources are tight sands, coal bed methane and shale gas.
Although these natural gas resources have historically been ignored in favor of conventional reserves, interest in these unconventional resources has grown in the last few years.
Nevertheless, in the context of wells exploiting these unconventional resources and/or in the context of non-vertical bore holes, liquid infiltration and stagnation may pose problems. In fact, the presence of these liquids significantly diminishes the yields of these wells.
Thus, a need exists for evacuating these liquids.
Methods enabling the evacuation of fluids (water, petroleum or a mixture of both) from the bottom of a well are designated by the generic term “artificial lift.” All of these methods are based on the same principle: If the energy contained in the tank is insufficient for lifting fluids without assistance, then it is useful to artificially lower the hydrostatic pressure or reduce the inner diameter of the well.
These methods include:                1) The “gas lift” method: Gas is continuously injected into the hydrostatic column, this lightens the column and enables fluid to lift. Having gas and compressors available at the surface is useful. When the oil/water proportion varies over time and as the tank pressure continues to reduce, then the gas injection point should be modified several times by means of well servicing. The “gas lift” method can be used in many situations (for ex., with a flow rate of 4,800 m3/day or with a drill depth of 4,600 m).        2) Methods using ESP (Electric Submersible Pump) pumps: These ESP pumps are positioned at the bottom of the well, within the liquid to be pumped. They create a depression in the well and a suction effect. These pumps require heavy and expensive equipment to be put in place and must be supplied with electricity from the surface. Possible flow rates can be varied (for ex., from tens of cubic meters per day to tens of thousands of cubic meters per day). Nevertheless, these pumps may not be primed if gas enters into the system (i.e., “gas lock”) and consequently, the evacuation of liquid will be compromised. These pumps are very prone to erosion and do not operate well if a gaseous fluid is present in the fluid, causing, for example, cavitation.        3) Methods using PCP (Progressive Cavity Pump) pumps: These pumps consist of a stator and a rotor. These pumps are positioned at the bottom of the well, within the liquid to be pumped, and must be supplied with electricity from the surface. Although these methods can be flexible, they do not enable all possible flow rates to be reached (up to 600 m3/day). In addition, the installation depths are limited (approximately 1,800 m). These pumps are very resistant to erosion and to the presence of solids, but certain aromatic compounds contained in hydrocarbons can damage the elastomer of the stator. In addition, these pumps are difficult to operate under polyphasic flow conditions.        4) Methods using “beam pumps.” Beam pumps are surface pumps that lift fluids in a cylinder from the well bottom. These methods are limited to low-yield wells (5 to 40 liters at each movement), and can be locked by the gas lock phenomenon (if gas enters into the system, no or little liquid can be lifted, because gas is compressible, unlike liquid). Power is required at the surface to operate the pump. In addition, these pumps are difficult to operate in inclined or horizontal wells.        5) Injection of surfactants at the well bottom that mix with liquid and form a foam, thereby lowering the hydrostatic pressure.        6) Installation of small-diameter tubing into the well (for ex. “velocity string” or “capillary string”): This tubing increases the velocity of the gas rising to the surface and, consequently, its liquid driving power. Installing this tubing requires that the full well completion design be overhauled (a potentially major operation). In addition, this installation cannot be a long-term solution, because as the tank pressure lowers, even a small diameter can be insufficient to create a sufficient velocity to evacuate liquids.        
Such methods are not free from faults, as indicated previously.
In addition, whereas historically gas wells were vertical, the development of unconventional resources was only made possible by drilling inclined or horizontal wells.
All the methods previously presented, if they are applicable to vertical wells, cannot be easily applicable to inclined or horizontal wells. In particular, methods comprising pumps activated by rods placed under rotation or traction from the surface can be difficult to implement in deviated wells.
Therefore a need exists for a method to evacuate liquids in wells that is inexpensive, simple to implement and strong.